JP4850850B2 - Display element driving method, display element, and electronic terminal - Google Patents

Description

  The present invention relates to a display element driving method, a display element, and an electronic terminal, and more particularly, to a display element driving technique for still image display including cholesteric liquid crystal.

  In recent years, development of electronic paper has been actively promoted in research institutions such as companies and universities. As an application market in which electronic paper is expected, various application forms such as a sub display of a mobile terminal and a display unit of an IC card have been proposed, starting with an electronic book.

  Conventionally, a cholesteric liquid crystal is known as a leading electronic paper. This cholesteric liquid crystal has excellent characteristics such as semi-permanent display retention (memory property), vivid color display, high contrast and high resolution. Furthermore, the cholesteric liquid crystal can display a vivid full color by laminating display layers exhibiting RGB reflection colors.

  By the way, since the cholesteric liquid crystal is a liquid crystal having a memory property, an inexpensive simple matrix drive is possible, and for example, an enlargement of A4 size or larger is relatively easy. The cholesteric liquid crystal consumes power only when the display content is updated (image rewriting), and when the image rewriting is completed, the image is held as it is even if the power is turned off.

  First, an example of driving a cholesteric liquid crystal as an example of a display element according to the present invention will be described.

  1A and 1B are diagrams for explaining the alignment state of the cholesteric liquid crystal. FIG. 1A shows a planar state, and FIG. 1B shows a focal conic state.

  A cholesteric liquid crystal can take two stable states, a planar state and a focal conic state, under no electric field.

  That is, as shown in FIG. 1A, since the incident light is reflected by the liquid crystal in the planar state, the human eye can see the reflected light.

  Further, as shown in FIG. 1B, in the focal conic state, incident light passes through the liquid crystal. Then, by providing a light absorption layer separately from the liquid crystal layer, black can be displayed in the focal conic state.

  Here, in the planar state, light having a wavelength corresponding to the helical pitch of the liquid crystal molecules is reflected, and the wavelength λ at which the reflection is maximized is λ = when the average refractive index of the liquid crystal is n and the helical pitch is p. It is indicated by n · p. Note that the reflection band Δλ increases with the refractive index anisotropy Δn of the liquid crystal.

  2A, 2B, and 2C are diagrams showing voltage characteristics (relationship between time and voltage) for driving the cholesteric liquid crystal. The electric field applied to the liquid crystal and each of the homeotropic state, the focal conic state, and the planar state are shown. It shows the state of change. Here, the homeotropic state is H, the focal conic state is FC, and the planar state is P.

  First, when a strong electric field is applied to the cholesteric liquid crystal, the helical structure of the liquid crystal molecules is completely unwound, and all molecules enter a homeotropic state H that follows the direction of the electric field.

  As shown in FIG. 2B, when the electric field is suddenly reduced to zero from the homeotropic state H, the spiral axis of the liquid crystal becomes perpendicular to the electrode, and the planar state P in which light is selectively reflected according to the spiral pitch is obtained.

  On the other hand, as shown in FIG. 2A, when the electric field is removed after the formation of a weak electric field that can finally unwind the liquid crystal molecules, or as shown in FIG. When removed, the spiral axis of the liquid crystal is parallel to the electrode, resulting in a focal conic state FC that transmits incident light.

  Further, if an electric field having an intermediate strength is applied and removed rapidly, the liquid crystal in the planar state P and the focal conic state FC is mixed, and halftone display becomes possible.

  Thus, the cholesteric liquid crystal is bistable, and information can be displayed using this phenomenon.

  FIG. 3 is a diagram showing the reflectance characteristics (the relationship between the voltage and the reflectance) of the cholesteric liquid crystal, and collectively shows the voltage responsiveness of the cholesteric liquid crystal described with reference to FIGS. 2A to 2C.

  As shown in FIG. 3, when the initial state is the planar state P (the portion with high reflectivity at the left end in FIG. 3), when the pulse voltage is raised to a certain range, the focal conic state FC (the portion with low reflectivity in FIG. 9) ), And when the pulse voltage is further increased, the driving band for the planar state P (the portion with the highest voltage at the right end) is reached again.

  When the initial state is the focal conic state FC (the leftmost portion having a low reflectance), the driving band for the planar state P is gradually increased as the pulse voltage is increased.

  In the planar state P, only the right circularly polarized light or the left circularly polarized light is reflected, and the remaining circularly polarized light is transmitted. Therefore, the maximum theoretical reflectance is 50%.

  By the way, conventionally, although it is related to the multiplex driving method of the element using the ferroelectric liquid crystal, the voltage fluctuation of the high-frequency AC waveform due to the influence of the signal electrode waveform in the non-selection period is a composite waveform applied to the liquid crystal element. However, there has been proposed a method of reducing the cost of the driver by driving at a low voltage (see, for example, Patent Document 1). The “non-selection period” in Patent Document 1 is, in other words, “non-selection pixel” during writing (synchronized with writing), and is not in a phase (asynchronous) completely independent from writing. .

  Further, conventionally, in order to uniformly align the liquid crystal, a driving method of a liquid crystal element having a memory property in which an erasing pulse is applied outside the selection period so that a good contrast can be maintained for a long time has been proposed. (For example, refer to Patent Document 2). The “erasing pulse applied outside the selection period” in Patent Document 2 is a reset pulse for uniformly aligning the liquid crystal and is given in synchronization with image writing. Asynchronous and does not suppress excessive power consumption.

Japanese Unexamined Patent Publication No. 63-293531 Japanese Patent Application Laid-Open No. 07-140443

  As described above, in recent years, electronic paper is being put into practical use using, for example, cholesteric liquid crystal.

  By the way, many electronic papers perform simple matrix driving with an inexpensive general-purpose driver. For example, there is a problem that an excessive inrush current occurs immediately after power is turned on and image rewriting (writing) is started. . Due to this inrush current, the battery is consumed rapidly, and further, the inrush current may exceed the supply current of the battery, which may cause the rewrite operation to stop or malfunction.

  Therefore, as a result of intensive studies on the cause of excessive inrush current immediately after the above-described power supply is turned on and image rewriting is started, the scan driver's shift register becomes indefinite after power-on, and excess electrodes It became clear that the main cause was that I chose.

  4A and 4B are diagrams for explaining problems in a conventional display element driving method. 4A shows an example of an image displayed so far, and FIG. 4B schematically shows a state immediately after the power is turned on and image rewriting is started.

  Conventionally, for example, a general-purpose driver used for, for example, an STN (Super Twisted Nematic) liquid crystal display element is usually used to display a moving image, so that a shift register of a scanning driver (scan driver) becomes indefinite. When the surplus electrode is selected, even if the first frame is scanned with the surplus electrode selected, there is no problem because the time during which the inrush current flows is very short.

  However, as shown in FIG. 4B, when the general-purpose driver as described above is applied to a still image display element such as electronic paper using cholesteric liquid crystal, for example, scanning speed is low in electronic paper ( For example, since one frame is scanned for about 1 second), the scanning time is increased while the above-described excessive electrode selection is performed, and a large current (inrush current) flows.

  Here, when rewriting of an image is started by turning on the power, the number of extra electrodes that are selected because the shift register of the general-purpose driver on the scanning side is in an indefinite state is, for example, 1 of all the scan electrodes The current (inrush current) flowing at that time is about several hundred milliamperes, for example.

  It should be noted that the phenomenon such as selection of excessive electrodes due to the use of such a general-purpose driver is not only when the power of electronic paper or the like is actually turned on, but also when the power is already turned on, the image is rewritten. In some cases, for example, the power to the general-purpose driver is cut off when displaying the image so far, and the power is supplied to the general-purpose driver again when the image is rewritten. That is, for example, when power that has been once cut off is supplied to the scan driver again, the shift register of the scan driver becomes indeterminate and excessive electrodes are selected, resulting in a large inrush current flowing. Become.

  The inrush current at the time of turning on the power described above becomes even larger particularly in the case of a large display such as A4 or a poster size, and this inrush current makes it difficult to drive the battery, or the drive voltage becomes unstable. This can cause problems such as display unevenness.

  The present invention has been made in view of the above-described problems of the conventional display element, and an object thereof is to provide a display element driving method, a display element, and an electronic terminal capable of suppressing a large inrush current generated immediately after image writing. Furthermore, the present invention provides a display device that enables the use of an inexpensive general-purpose driver and battery drive by suppressing a large inrush current that occurs immediately after image writing, and further enables power saving and stable display quality. An object is to provide a driving method, a display element, and an electronic terminal.

According to a first aspect of the present invention, it includes a plurality of scan electrodes and a plurality of data electrodes that intersect at opposite state, a driving method of a display device which performs writing processing of the image of the scan electrodes to select Then, before performing the image writing process , a blank scan process is performed in which each scan electrode is scanned while applying a plurality of pulses at intervals shorter than the pulse interval in the writing process. An element driving method is provided.

According to a second aspect of the present invention, includes a plurality of scan electrodes and a plurality of data electrodes that intersect at opposite state, the scan electrodes is by Ri selection scan driver, and the respective data electrode and other data signals provided by the data driver in response to the scan electrodes the selected a display device writing processing of the image is performed, the scan driver, before performing the write process of said image, said writing There is provided a display element characterized in that a blank scan process is performed in which each scan electrode is scanned while applying a plurality of pulses at intervals shorter than the pulse interval in the process .

According to a third aspect of the present invention, includes a plurality of scan electrodes and a plurality of data electrodes that intersect at opposite state, the scan electrodes is by Ri selection scan driver, and the respective data electrode and other data signals provided by the data driver in response to the scan electrodes the selected a display device writing processing of the image is performed, the scan driver, before performing the write process of said image, said writing the scanning each scan electrodes while applying a plurality of pulses at intervals shorter than the pulse interval in the processing, electronic terminal, characterized in that the application of the display device for executing the empty scan process is provided.

  That is, the present inventors scan a predetermined number of lines at high speed (empty scan) while suppressing the voltage output for driving the display medium in order to eliminate the indefinite state of the scan driver after power-on at high speed. And found that the inrush current can be greatly suppressed.

At this time, it is preferable to output non-selected data from the data driver in synchronization.
As a result, by performing an empty scan instantly without causing discomfort to the user, inrush current due to excessive scan line selection can be significantly suppressed, and subsequent stable driving can be realized. .

  ADVANTAGE OF THE INVENTION According to this invention, the drive method of a display element, a display element, and an electronic terminal which can suppress the big inrush current which arises immediately after the image writing can be provided. Furthermore, according to the present invention, it is possible to use an inexpensive general-purpose driver and to drive a battery by suppressing a large inrush current that occurs immediately after image writing, and to achieve power saving and stable display quality. An element driving method, a display element, and an electronic terminal can be provided.

  First, the principle of the display element driving method according to the present invention will be described with reference to FIGS. 5A to 5C. FIG. 5A shows an example of an image displayed so far, and FIG. 5B schematically shows an empty scan performed immediately after the power is turned on and image writing (rewriting) is started. FIG. 5C shows how an actual image is written after the blank scan.

  As shown in FIG. 5B, the display element driving method according to the present invention performs an empty scan process on the scan electrodes before performing the image writing process, and then performs an actual scan process as shown in FIG. 5C. An image writing process is performed.

  As a result, it is possible to prevent the shift register of the scan driver from being in an indefinite state and selecting an excessive electrode, thereby preventing a large inrush current from flowing.

  Hereinafter, embodiments of a display element driving method, a display element, and an electronic terminal according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 6 is a block diagram schematically showing an embodiment of an electronic terminal (display device) to which the display element according to the present invention is applied. In FIG. 6, reference numeral 1 is a display element, 3 is a power supply circuit, 4 is a control circuit, 21 is a driver IC (scan driver) on the scanning side, and 22 is a driver IC (data driver) on the data side. . Here, the scan driver 21 shown in FIG. 6 shows the first embodiment of the scan driver of the present invention, and has a number of control terminals equal to the number of scan electrodes in the display element 1.

  As shown in FIG. 6, the power supply circuit 3 includes a booster 31, a voltage generator 32, and a regulator 33. For example, the booster 31 receives an input voltage of about +3 to +5 V from the battery, boosts the voltage to drive the display medium (display element 1), and supplies the boosted voltage to the voltage generator 32. The voltage generation unit 32 generates necessary voltages for the scan driver 21 and the data driver 22 respectively, and the regulator 33 stabilizes the voltage from the voltage generation unit 32 and supplies it to the scan driver 21 and the data driver 22. .

  The control circuit 4 includes a calculation unit 41, a control data generation unit 42, and an image data generation unit 43. The calculation unit 41 calculates image data and control signals supplied from the outside, and the image data is supplied to the data driver 22 as data suitable for the display element 1 via the image data generation unit 43, and the control signal Are supplied to the scan driver 21 and the data driver 22 as various control signals suitable for the display element 1 via the control signal generation unit 42.

  Here, as a control signal supplied from the control signal generation unit 42 to the scan driver 21 and the data driver 22, for example, a pulse polarity control signal CS2 for inversion control of the polarity of the pulse voltage applied to the display element 1, an image of one frame. A frame start signal CS3 indicating the start of the data, a line in which data is stored by the data driver 22 and a data latch / scan shift signal CS4 for controlling the synchronization of the line selected by the scan driver 21, and the data driver 22 and the scan driver 21 And a driver output cutoff signal CS5 for cutting off the driver output. In addition, a data capturing clock CS1 for sequentially capturing data for one line is also supplied from the control signal generation unit 42 to the data driver 22.

  The display element driving method according to the present invention is realized by devising a sequence in the control circuit 4 for controlling display contents.

  FIG. 7 is a cross-sectional view schematically showing an example of the display element (liquid crystal display element) shown in FIG. In FIG. 7, reference numerals 11 and 12 are film substrates, 13 and 14 are transparent electrodes (for example, ITO), 15 is a liquid crystal composition (cholesteric liquid crystal), 16 and 17 are sealing materials, 18 is a light absorbing layer, and Reference numeral 19 denotes a drive circuit.

  The display element 1 includes a liquid crystal composition 15, and transparent electrodes 13 and 14 that intersect perpendicularly are formed on the inner surfaces of the transparent film substrates 11 and 12 (surfaces in which the liquid crystal composition 15 is sealed), respectively. ing. That is, a plurality of scan electrodes 13 and a plurality of data electrodes 14 are formed in a matrix on opposing film substrates 11 and 12. In FIG. 7, the scan electrode 13 and the data electrode 14 are drawn so as to be parallel at first glance. However, actually, for example, a plurality of data electrodes 14 intersect with one scan electrode 13. Needless to say. Furthermore, the thickness of each film substrate 11 and 12 is, for example, about 0.2 mm, and the thickness of the liquid crystal composition 15 is, for example, about 3 μm to 6 μm. Their ratio is ignored.

  Here, the electrodes 13 and 14 are preferably coated with an insulating thin film or an alignment stabilizing film. Further, a visible light absorption layer 18 is provided on the outer surface (back surface) of the substrate (12) opposite to the side on which light is incident, if necessary.

  In this example, the liquid crystal composition 15 is a cholesteric liquid crystal exhibiting a cholesteric phase at room temperature, and these materials and combinations thereof will be specifically described by the following experimental examples.

  The sealing materials 16 and 17 are for sealing the liquid crystal composition 15 between the film substrates 11 and 12. The drive circuit 19 is for applying a predetermined pulse voltage to the electrodes 13 and 14.

  Although the film substrates 11 and 12 both have translucency, at least one of the pair of substrates that can be used as the display element 1 of this embodiment needs to have translucency. It is. In addition, although a glass substrate can be illustrated as a board | substrate which has translucency, flexible resin film substrates, such as PET and PC, can be used besides a glass substrate. In addition, as the electrodes 13 and 14, for example, ITO (Indium Tin Oxide) is representative, but in addition, for example, a transparent conductive film such as IZO (Indium Zinc Oxide). Alternatively, a metal electrode such as aluminum or silicon, or a photoconductive film such as amorphous silicon or BSO (Bismuth Silicon Oxide) can be used.

  In the liquid crystal display element shown in FIG. 7, as described above, a plurality of strip-like transparent electrodes 13 and 14 parallel to each other are formed on the inner surfaces of the transparent film substrates 11 and 12, and these electrodes 13 and 14 are formed on the substrate. They face each other so as to intersect each other when viewed from a direction perpendicular to the direction.

  In the display element according to the present invention, an insulating thin film having a function of preventing a short circuit between the electrodes or improving the reliability of the liquid crystal display element as a gas barrier layer may be formed. Examples of the orientation stabilizing film include organic films such as polyimide resin, polyamideimide resin, polyetherimide resin, polyvinyl butyral resin, and acrylic resin, or inorganic materials such as silicon oxide and aluminum oxide. The alignment stabilizing film coated on the electrodes 13 and 14 can also be used as an insulating thin film.

  The liquid crystal display element according to the present invention may be provided with a spacer between the pair of substrates for uniformly holding the inter-substrate gap. Examples of the spacer include F spheres made of resin or inorganic oxide. Further, a fixed spacer whose surface is coated with a thermoplastic resin can also be suitably used.

  The substance constituting the liquid crystal composition (liquid crystal layer) 15 is, for example, cholesteric liquid crystal obtained by adding 10 to 40 wt% of a chiral agent to the nematic liquid crystal composition. Here, the addition amount of the chiral agent is a value when the total amount of the nematic liquid crystal component and the chiral agent is 100 wt%.

  Various types of conventionally known nematic liquid crystals can be used as the nematic liquid crystal, but a dielectric anisotropy of 20 or more is preferable for the convenience of driving voltage. That is, when the dielectric anisotropy is 20 or more, the driving voltage is relatively low. The dielectric anisotropy (Δε) of the cholesteric liquid crystal composition is preferably 20-50. Within this range, general-purpose drivers can be used.

  The refractive index anisotropy (Δn) is preferably 0.18 to 0.24. If it is smaller than this range, the reflectivity in the planar state is lowered, and if it is larger than this range, the scattering reflection in the focal conic state is increased and the viscosity is increased and the response speed is lowered. The thickness of the liquid crystal is preferably about 3 μm to 6 μm. If it is smaller than this, the reflectivity in the planar state becomes low, and if it is larger than this, the driving voltage becomes too high.

  An A4-sized QVGA display element 1 having the above-described configuration was manufactured. The display element 1 has a three-layer laminated structure exhibiting RGB reflection colors, and can perform display close to full color.

  At this time, the stacking order is preferably B (blue), G (green), and R (red) in order from the observation direction, and the polarization state of the reflected light of G arranged in the middle is opposite to that of B and R. It is preferable that the reflection efficiency is further improved. Specifically, for example, when B and R reflect right circular polarization, G is preferably left circular polarization, and conversely, when B and R reflect left circular polarization, G is right circular polarization. Preferably there is. The polarization state of the reflected light can be controlled by changing the chiral agent to R form or S form (L form).

  Then, the above-described color QVGA elements were arranged in a tile shape, and a large display element was prototyped. At this time, by using a common scan driver for each of the RGB layers, an increase in cost can be suppressed. Here, the driver IC uses a general-purpose STN driver, for example, 320 outputs (using two 160-output driver ICs) on the data side and 240 outputs (one 240-driver output IC) The driving circuit is configured on the scanning side.

  At this time, it is preferable that the voltage input to the driver is stabilized by a voltage follower of an operational amplifier as necessary. A battery was used as the battery.

The conventional driving method and the driving method according to the present invention are applied to the display element described above.
First, when the display element was driven by a conventional sequence, an inrush current flowed about 800 mA, the battery current supply could not catch up due to the overcurrent, and the display was far from the original contrast, resulting in a low quality display.

  On the other hand, when the display element was driven according to the sequence of the present invention, the inrush current was suppressed to 300 mA or less, the driving voltage was stabilized, and the original display quality could be realized.

  FIG. 8 is a flowchart for explaining an example of the display element driving method according to the present invention.

  As shown in FIG. 8, first, the control unit voltage is raised in step ST1, then the liquid crystal drive voltage is raised in step ST2, and further, the scan driver performs an empty scan in step ST3, and then step ST4. Proceed to, and image rewriting (writing) is started. That is, for example, the indefinite state of the scan driver after power-on is eliminated by executing a blank scan before starting rewriting.

  Here, since the image data may be indefinite when the blank scan is executed in step ST3, it is not necessary to perform an image data input process. That is, even if the image data is indefinite (random), the voltage output at the time of the blank scan is not more than the threshold value at which the response starts, and thus there is no influence on the display quality.

  Then, after proceeding to step ST5 and completing the rewriting of the image, the control voltage is cut off at step ST6, and further the liquid crystal driving voltage is cut off.

  In the above, the empty scan in step ST3 may be, for example, the non-response region NR shown in FIG. 3, but preferably, the driver outputs a voltage output cutoff function (usually by DSPOF as shown in FIG. 9). If the voltage for driving the display medium is turned off using the function, it is more effective for power saving.

  FIG. 9 is a diagram showing control signals in an example of the display element driving method according to the present invention, and shows the use of the voltage output cutoff function of the driver used during the empty scan in step ST3 in FIG.

  As shown in FIG. 9, when the power is turned on and the power supply voltage Vp becomes Vcc, the signal / DSPOF becomes a low level “L” in the inrush current suppression phase P1, and the output of the driver is cut off. In this inrush current suppression phase P1, the data latch / scan pulse signal LPe is output, for example, for one frame, and the scan driver performs an empty scan. In the next writing phase P2, an image writing (rewriting) process similar to the conventional one is performed.

  FIG. 10 is a diagram for explaining scan pulse signals in the display element driving method according to the present invention. In FIG. 10, reference symbol XSCL indicates a driver clock for data capture, LPn indicates a scan pulse during a normal write operation, and LPe indicates a scan pulse during an empty scan.

  As shown in FIG. 10, during a normal write operation, during the time Td when the scan driver selects one scan electrode, for example, data corresponding to the next selected scan electrode is data according to the driver clock XSCL. A data pulse (voltage output) is applied to each of the plurality of data electrodes from the data driver in synchronization with selection of the scan electrode and selection of the scan electrode.

  Here, the interval (˜Td) of the scan pulse LPn during the normal write operation is, for example, about several hundred μsec. To several msec., Whereas the interval of the scan pulse LPe during the empty scan is 1 μsec. The following (for example, several hundred nsec.) Is preferable. That is, during a normal write operation, a time for writing data for one scan line or a time Td for reading data for the next one scan line (approximately the interval between scan pulses LPn) is several hundred μsec. To several msec. In contrast to the long time (low speed), the interval between the scan pulses LPe during the idle scan is preferably a short time (high speed) equivalent to that of the STN liquid crystal display element, such as 1 μsec or less.

  Accordingly, it is possible to perform the same image writing (rewriting) processing as before without causing the user to wait for the empty scan. According to the present embodiment, the indefinite state of the shift register of the scan driver is eliminated by the empty scan, and it is possible to avoid a large inrush current from flowing due to the selection of an excessive electrode.

  11A to 14 are views for explaining second to fifth embodiments of the scan driver to which the present invention is applied.

  11A and 11B are diagrams for explaining a second embodiment of the scan driver to which the present invention is applied. FIG. 11A shows a blank scan process, and FIG. 11B shows a normal image writing process. Yes.

  As shown in FIGS. 11A and 11B, the scan driver 210 of the second embodiment has control terminals equal to or more than the number of scan electrodes in the display element 1.

  As shown in FIG. 11A, the scan driver 210 according to the second embodiment writes an image immediately after power is turned on and an operable logic voltage is applied to the scan driver 210, for example. The empty scan processing performed before (rewriting) is performed on all the control terminals of the scan driver 210, thereby eliminating the indeterminate state of all the shift registers in the scan driver 210 and inrush current at the start of image writing. Is to minimize. In this case, since all the control electrodes of the scan driver 210 are scanned (empty scan), the time required for the blank scan is slightly longer than that of the third embodiment described below, but this is a serious problem. Absent.

  12A and 12B are diagrams for explaining a third embodiment of a scan driver to which the present invention is applied. FIG. 12A shows a blank scan process, and FIG. 12B shows a normal image writing process. Yes.

  As shown in FIGS. 12A and 12B, the scan driver 210 of the third embodiment also has control terminals equal to or more than the number of scan electrodes in the display element 1 as in the second embodiment described above. Yes.

  As shown in FIG. 12A, the empty scan process by the scan driver 210 of the third embodiment performs the empty scan of the scan driver 210 by the number of scan electrodes in the display element 1. At this time, some shift registers of the scan driver excluding the control terminals corresponding to the scan electrodes from all the control terminals in the scan driver 210 remain in an indefinite state, but the effect of reducing the inrush current at the time of image writing Is sufficient for practical use. According to the third embodiment, the time required for the blank scan at the time of image writing (before writing) can be made shorter than that of the second embodiment described above.

  Then, as shown in FIG. 12B, when image writing processing is performed, scanning is performed by the number of scan electrodes in the display element 1 to write actual images, and subsequently, to the remaining control terminals in the scan driver 210. On the other hand, an empty scan is performed, and the indefinite state of all the shift registers of the scan driver is eliminated. Note that the scan for writing images (write scan) is performed at a low speed, for example, so that the time required for the blank scan after the write scan at the time of actual image writing is hardly a problem. Absent.

  In the above, in the second embodiment shown in FIGS. 11A and 11B and the third embodiment shown in FIGS. 12A and 12B, the same scan driver 210 is used, and the control (sequence) is different. Can be realized.

  FIG. 13 is a diagram for explaining a fourth embodiment of a scan driver to which the present invention is applied.

  As shown in FIG. 13, the scan driver of the fourth embodiment is composed of two scan driver units 211 and 212 each having control terminals that is half the number of scan electrodes of the display element 1. . In the fourth embodiment, the empty scan processing by the two scan driver units 211 and 212 is sequentially performed on all the scan electrodes. As described above, when performing a blank scan process using a plurality of scan driver units (driver ICs) 211 and 212, for example, by performing sequentially for all the scan electrodes, the same as the actual image writing process. The empty scan process can be easily performed with this sequence.

  FIG. 14 is a diagram for explaining a fifth embodiment of a scan driver to which the present invention is applied.

  As shown in FIG. 14, the scan driver of the fifth embodiment includes two scan driver units 211 having control terminals that are half the number of scan electrodes of the display element 1, as in the fourth embodiment described above. 212, the empty scan processing by the two scan driver units 211 and 212 is performed in parallel for the corresponding half of the scan electrodes. As a result, the time required for the blank scan process can be reduced to about half that of the fourth embodiment described above. Note that the actual image writing process is sequentially performed on all the scan electrodes of the display element 1 in the same manner as the empty scan process shown in FIG.

  Of course, the number of scan units (driver ICs) constituting the scan driver is not limited to two.

  FIG. 15 is a diagram showing an example of a display element to which the present invention is applied. In FIG. 15, reference numeral 101 is a blue (B) layer that reflects blue light, 102 is a green (G) layer that reflects green light, 103 is a red (R) layer that reflects red light, and Reference numeral 104 denotes a black (K) layer that absorbs light.

  As shown in FIG. 15, the display element 1 has a structure in which an R layer 103, a G layer 102, and a B layer 101 are sequentially stacked on a K layer 104. The B layer 101 has a configuration in which the liquid crystal 113 is sandwiched between an opposing substrate (film substrate) and transparent electrodes (ITO) 111, 112, 115, and 114, and the G layer 102 has an opposing substrate and transparent electrodes 121, The liquid crystal 123 is sandwiched between 122, 125, and 124, and the R layer 103 is configured such that the liquid crystal 133 is sandwiched between the opposing substrate and the transparent electrodes 131, 132, 135, and 134.

  The transparent electrodes 112 and 114 of the B layer 101 are connected to the B layer control circuit 110, and the transparent electrodes 122 and 124 of the G layer 102 are connected to the G layer control circuit 120, and the R layer 103 The transparent electrodes 132 and 134 are connected to the R layer control circuit 130. The transparent electrodes 112, 114; 122, 124; 132, 134 in each layer constitute a scan electrode and a data electrode, respectively, and intersect each other in an opposing state. Note that in each of the layers 101 to 103, a scan driver is connected to the scan electrode, and a data driver is connected to the data electrode. With the above configuration, the display element 1 can perform display close to full color.

  In the above, the display element 1 is configured as, for example, an A6 size QVGA, and the stacking order of the B layer 101, the G layer 102, and the R layer 103, the polarization direction of the liquid crystal, the driver used, and the like are related to FIG. This is the same as the A4 size QVGA display element described above. In FIG. 15, control circuits (scan drivers) 130 to 110 for each layer of RGB are separately provided. However, the cost can be reduced by making the scan drivers (130 to 110) for each layer of RGB common. it can.

  FIG. 16 is a block diagram schematically showing another embodiment of an electronic terminal to which the display element of FIG. 15 is applied.

  As shown in FIG. 16, the electronic terminal (display device) 200 according to the present embodiment receives the clock CLK, display information, and driving power via an electromagnetic wave without contact with the reader / writer (electromagnetic wave source) 100 and receives an image. Is written (rewritten). The display device 200 includes an antenna 202, a rectifier circuit 203, a control circuit 210, and a display element 201 having a B layer 211, a G layer 212, and an R layer 213. Here, the control circuit 210 corresponds to a combination of the B layer control circuit 110, the G layer control circuit 120, and the R layer control circuit 130 in FIG.

  Note that it is preferable to use a Zener diode or the like in order to stabilize the voltage input to the control circuit (driver) 210 with low power consumption as necessary.

  In the display device 200 according to the present embodiment, for example, writing of the display element (display unit) 201 is started by holding the reader / writer 100, and writing is ended when the display device 200 is held over the reader / writer 100. The display image is retained.

  When the display device 200 shown in FIG. 16 is driven by the conventional sequence over the reader / writer 100, an inrush current larger than the energy that can be supplied from the electromagnetic wave flows, a voltage drop occurs, and a satisfactory display cannot be obtained. Specifically, the voltage drop occurs, so that the pixel that should be in the planar state is not in the planar state, but is in a dark display, resulting in a low-quality display that is far from the original contrast.

  On the other hand, when the display element driving method according to the present invention is applied, the inrush current is almost suppressed immediately after the display device 200 is held over the reader / writer 100, and the driving voltage is stabilized and the original display quality is maintained. Was able to be realized.

  Here, in the battery-less display device, the blank scan speed can be approximately 1 μsec. / Line or less (for example, several hundred nsec./line) depending on the performance of the driver used. The writing speed is generally, for example, several msec./line or more. Note that the speed ratio between the blank scan and the image writing scan can vary depending on various conditions. However, for example, the ratio of the blank scan speed / image writing speed is the balance with the waiting time required for the blank scan. 100 times or more is preferable.

  As described above, the display element according to the present invention does not include a battery as shown in FIG. 16, and a battery-less display that wirelessly receives power supply from the reader / writer 100 together with display information (written image data). The present invention can also be applied to the apparatus 200. That is, as in the present invention, the scan driver is executed before receiving the image data and power supplied from the reader / writer 100 and writing of the image is started, thereby eliminating the indeterminate state of the scan driver and causing a large inrush current. Can be prevented from flowing and image writing can be executed.

  The present invention can be applied not only to cholesteric liquid crystals but also to all display elements that perform writing at low speed for still image display such as electronic paper, and suppresses a large inrush current that occurs immediately after image writing. Accordingly, it is possible to provide a display element driving method, a display element, and an electronic terminal that enable use of an inexpensive general-purpose driver and battery driving, and further achieve power saving and stable display quality.

It is FIG. (1) for demonstrating the orientation state of a cholesteric liquid crystal. FIG. 3 is a diagram (part 2) for explaining the alignment state of the cholesteric liquid crystal. FIG. 3 is a diagram (part 1) illustrating voltage characteristics for driving a cholesteric liquid crystal. FIG. 6 is a diagram (part 2) illustrating voltage characteristics for driving a cholesteric liquid crystal. FIG. 6 is a diagram (part 3) illustrating voltage characteristics for driving a cholesteric liquid crystal. It is a figure which shows the reflectance characteristic of a cholesteric liquid crystal. It is FIG. (1) for demonstrating the subject in the drive method of the conventional display element. It is FIG. (2) for demonstrating the subject in the drive method of the conventional display element. It is FIG. (1) for demonstrating the principle of the drive method of the display element which concerns on this invention. It is FIG. (2) for demonstrating the principle of the drive method of the display element which concerns on this invention. It is FIG. (3) for demonstrating the principle of the drive method of the display element which concerns on this invention. It is a block diagram which shows roughly one Example of the electronic terminal to which the display element which concerns on this invention is applied. It is sectional drawing which shows roughly an example of the display element shown in FIG. 3 is a flowchart for explaining an example of a display element driving method according to the present invention. It is a figure which shows the control signal in an example of the drive method of the display element which concerns on this invention. It is a figure for demonstrating the scan pulse signal in the drive method of the display element which concerns on this invention. It is FIG. (1) for demonstrating the 2nd Example of the scan driver to which this invention is applied. It is FIG. (2) for demonstrating the 2nd Example of the scan driver to which this invention is applied. It is FIG. (1) for demonstrating the 3rd Example of the scan driver to which this invention is applied. It is FIG. (2) for demonstrating the 3rd Example of the scan driver to which this invention is applied. It is a figure for demonstrating the 4th Example of the scan driver to which this invention is applied. It is a figure for demonstrating the 5th Example of the scan driver to which this invention is applied. It is a figure which shows an example of the display element to which this invention is applied. FIG. 16 is a block diagram schematically showing another embodiment of an electronic terminal to which the display element of FIG. 15 is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display element 3 Power supply circuit 4 Control circuit 11, 12 Film board | substrate 13, 14 Transparent electrode (ITO)
15 Liquid crystal composition (cholesteric liquid crystal)
16, 17 Sealing material 18 Light absorption layer 19 Drive circuit 21 Driver IC (scan driver) on the scanning side
22 Data side driver IC (data driver)
31 Boosting Unit 32 Voltage Generation Unit 33 Regulator 41 Calculation Unit 42 Control Signal Generation Unit 43 Image Data Generation Unit 100 Reader / Writer (Electromagnetic Wave Source)
101, 211 Blue (B) layer 102, 212 Green (G) layer 103, 213 Red (R) layer 104 Black (K) layer 110 Blue (B) layer control circuit 120 Green (G) layer control circuit 130 Red (R) Layer Control Circuit 200 Electronic Terminal (Display Device)
202 Antenna 203 Rectifier circuit 210 Control circuit FC Focal conic state H Homeotropic state P Planar state

Claims (20)

Comprising a plurality of scan electrodes and a plurality of data electrodes that intersect at opposite state, a the scan electrode by selecting a display element drive method performing write processing of the image,
Before performing the image writing process, an empty scan process is performed in which each scan electrode is scanned while applying a plurality of pulses at intervals shorter than the pulse interval in the writing process. Driving method. The display element driving method according to claim 1,
The display device driving method, wherein the image writing process is performed by applying a pulsed driving voltage to a display medium between the selected scan electrode and the plurality of data electrodes. The display element driving method according to claim 2,
In the empty scan process, the voltage output applied to the display medium is equal to or lower than the response value voltage of the display medium. The display element driving method according to claim 3,
In the empty scan process, the voltage output of a data driver that drives the plurality of data electrodes is in an indefinite state. The display element driving method according to claim 3,
In the empty scan process, the voltage output applied to the display medium is zero. The display element driving method according to claim 5,
In the empty scan process, the voltage output of a data driver that drives the plurality of data electrodes is turned off. The display element driving method according to claim 1,
The display element driving method, wherein the empty scan process is performed immediately after an operable logic voltage is applied to a scan driver that sequentially selects the plurality of scan electrodes. The display element driving method according to claim 1,
A display element driving method, wherein a scanning speed of the blank scanning process is higher than a scanning speed of the image writing process. The display element driving method according to claim 1,
A display element driving method, wherein the display medium has a memory property. The display element driving method according to claim 9,
A display element driving method, wherein the display medium uses a liquid crystal forming a cholesteric phase. Comprising a plurality of scan electrodes and a plurality of data electrodes that intersect at opposite state, the scan electrodes are-option election Ri by the scan driver, and the respective data electrode data corresponding to the scan electrodes the selected A display element on which a data signal is given by a driver and image writing processing is performed,
The scan driver performs a blank scan process of scanning each scan electrode while applying a plurality of pulses at an interval shorter than the pulse interval in the write process before performing the image write process. A display element. The display device according to claim 11,
The display device, wherein the scan driver performs the empty scan process immediately after a logic voltage operable to the scan driver is applied. The display device according to claim 11,
The display device, wherein the scan driver performs the blank scan process at a scan speed faster than a scan speed in the image writing process. The display device according to claim 11,
The display element, wherein the display medium has a memory property. The display element according to claim 14, wherein
A display element using liquid crystal forming a cholesteric phase as the display medium. The display element according to claim 15, wherein
The display element has a laminated structure of a plurality of display element units having different reflected light. The display element according to claim 16, wherein
The display device, wherein the scan driver drives a corresponding scan electrode of each display element unit in common. The display device according to claim 11,
The display element, wherein the scan driver and the data driver are general-purpose drivers.   An electronic terminal to which the display element according to any one of claims 11 to 18 is applied. The electronic terminal according to claim 19,
The electronic terminal is a battery-less display device that receives a clock, display information, and driving power from a reader / writer and writes an image.

Images